I've just finished doing some checks about Team Viewer 14 (TV14) Linux version and HiDPI.
Version 14 is different, compared to previous version. In version 14 the app is using QT for GUI and it also adhere to QT Strings to override configuration, so if you have a 4K screen for example and you run TV14 without any parameters, it will try to scale up to the system's scaling settings, which will show a weird GUI to the point of uselessness.
What can be done? You can scale it to 1.0 to 2.0 by editing the file /opt/teamviewer/tv_bin/script/tvw_config (as root) and add at the bottom of the file the following line:
Save and exit. When launching Teamviewer - you'll get it at twice the size. You can change the 2 to 1 to get it at the correct (small) size.
The missing thing that is needed - is that the dev team of Teamviewer change the GUI code to HiDPI and dynamic scaling, as explained by Trolltech here.